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What are Microdata?
Microdata files from the American Community Survey show the full range of responses made on individual questionnaires. For example, how one household or one household member answered questions on occupation, place of work, and so forth. The files contain records for a sample of all housing units, with information on the characteristics of each unit and the people in it.
All identifying information is removed to ensure confidentiality. The records selected are a sample of those households that received the questionnaire. The questionnaire included questions on age, sex, tenure, income, education, language spoken at home, journey to work, occupation, condominium status, shelter costs, vehicles available, and other subjects. For more information click on the following link: Subjects in the American Community Survey PUMS datasets
The full range of population and housing information collected in the American Community Survey is available in the PUMS: For most questions asked on the questionnaire, the response is given in these files -- and you design tabulations to aggregate the responses in ways that are useful to you.Summary Data and Microdata -- What's the Difference?
Summary data are predefined cross tabulations of characteristics. The basic unit of analysis is a specific geographic entity -- state, county, etc. -- for which estimates of persons, families, households, or housing units in particular categories are provided.
In microdata, the basic unit is an individual housing unit and the people who live in it. The record shows all the information associated with a specific housing unit except for names, addresses, or other identifying information.
It is you, the user, who determines the structure of the tabulation and the characteristics to be tabulated. Only large geographic areas are identified on microdata records -- in the case of the American Community Survey, states. The Census Bureau uses a minimum population threshold to help avoid disclosure of information about any household or individual.
To further protect confidentiality, there is limited detail on items such as place of residence, place of work, high incomes, and other items.Why Use PUMS?
For many data users, the summary tables and tabular and narrative profile reports will suffice. Microdata are for those users who want to create do-it-yourself tabulations, to be able to further draw on the richness of detail recorded in the survey.
Help With Using PUMS!
PUMS estimates for selected housing and population characteristics are included here to assist data users in determining that they are correctly using the weights to compute estimates. These estimates are referred to as PUMS Control Counts. Data users who have doubts about the way they are computing estimates should attempt to reproduce the estimates that are provided in one of the following files.
Note that some of these estimates may be different from the estimates for the same characteristics published in the American FactFinder. For an explanation of these differences, see the 2003 Accuracy of the PUMS document.
Microdata users frequently want to look at relationships among variables not shown in the standard products offered by the Census Bureau. For example, what are the characteristics of unemployed homeowners? What characteristics do families with four or more children have in common? What kinds of Hispanic families in a state own their own homes?
The advantage of PUMS is that data users can tabulate data according to the characteristics they need to know about. The American Community Survey PUMS are useful for research that does not require the identification of geographic areas smaller than states.
PUMS files are perfect for people, such as students, who are looking for greater accessibility to inexpensive data for research projects. Data users in academic life -- economists, psychologists, and sociologists -- have found the PUMS useful for regression analysis and modeling applications.PUMS Records
There are two basic record types: the housing unit record and the person record. Each has a unique identifier. Each of the records contains a serial number that links the persons in the housing unit to the proper housing unit record. The file is sorted to maintain the relationship between both record types.
The Census Bureau releases the PUMS in this format because of the tremendous amount of data contained in one record. Although these records are extremely large, they can be handled by most statistical or report-writing software. Each record has an individual weight which allows users to produce population estimates close to those in other products showing sample data.